inline constant return from error() function

Commit e208f9c introduced a macro to turn error() calls
into:

  (error(), -1)

to make the constant return value more visible to the
calling code (and thus let the compiler make better
decisions about the code).

This works well for code like:

  return error(...);

but the "-1" is superfluous in code that just calls error()
without caring about the return value. In older versions of
gcc, that was fine, but gcc 4.9 complains with -Wunused-value.

We can work around this by encapsulating the constant return
value in a static inline function, as gcc specifically
avoids complaining about unused function returns unless the
function has been specifically marked with the
warn_unused_result attribute.

We also use the same trick for config_error_nonbool and
opterror, which learned the same error technique in a469a10.

Reported-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/parse-options.h b/parse-options.h
index d670cb9..1ef8da1 100644
--- a/parse-options.h
+++ b/parse-options.h
@@ -180,7 +180,7 @@ extern NORETURN void usage_msg_opt(const char *msg,
 extern int optbug(const struct option *opt, const char *reason);
 extern int opterror(const struct option *opt, const char *reason, int flags);
 #if defined(__GNUC__) && ! defined(__clang__)
-#define opterror(o,r,f) (opterror((o),(r),(f)), -1)
+#define opterror(o,r,f) (opterror((o),(r),(f)), const_error())
 #endif
 
 /*----- incremental advanced APIs -----*/